I’ve argued in recent posts that the Christmas period would leave us a little blind as to what is happening in terms of the Omicron variant. The optimist in me saw some signs both from the data here and what we’d seen happen in South Africa that the wave might be slowing down going into Christmas. However whether or not this slowdown was real and sustained would not be immediately clear until after Christmas.
There were a couple of reasons for that.
- Data reporting would be patchy through the Christmas period. We would have days with no or little reporting followed by over reporting.
- Behaviours would change over Christmas. On the one hand people would be on holiday and schools would break up. This would act as a bit of a circuit break for some communities. On the other hand, we’d also see a lot of extra mixing for parties, nights out and family get togethers with in effect a double festival including the New Year. In effect, we may have a COVID wave/spike within the wave.
- At the same time hospital data may also get disrupted at such a time. People may be more reluctant to go into hospital over a festive period, prolonging admission leading to more people who are even sicker being admitted on the days following bank holidays. Additionally holiday periods and staffing pressure may lead to a slowdown in discharging patients from the wards. This will make it harder for us to conclude about disease severity from length of stay and inpatient data.[1]
Another factor has been at work. There has been a surge in demand for LFT and PCR tests and that may well mean that we have caught a lower percentage of cases. We start from the assumption that not all cases are caught through testing both because not everyone takes a test and because there will be a percentage of false negatives for various reason. So, a big clue is whether or not test positivity is stable or not.
There is clearly a challenge at the moment with supply of test kits and that will affect capacity and therefore the number of cases caught. However, on the flip side, we probably were at the stage where we were catching as many cases as we were likely to and this has probably been helped by the wave coinciding with winter cold bugs with similar symptoms leading to more people testing who may well have been asymptomatic had they not also caught colds at the same time. This may mean that we’ve actually caught a higher percentage of infections in the case reporting in the lead up to Christmas.
But all of this means that it has been harder to say for certain what the case numbers have been doing over the past week or two. The dat through next week will probably give us a clearer picture as we move out of the holiday period and supply catches up with demand for tests. Expect another large spike in case numbers on Wednesday as schools are required to test all returning pupils. Then later in the week we’ll see the truer picture. My own rule of thumb is that if the average number of cases is over 225,000 by Friday then we are still seeking exponential growth, anything under 200,000 will suggest that the increase has continued to slow down after Christmas.
In terms of hospitalisations, this is always a lag measure, partly because of admissions being between 6-10 days after testing positive and partly because the data reporting tends to lag behind significantly. The UK data at the moment only goes up to the 27th December. This doesn’t look too bad with admissions averaging at 1416 on the 27th. This translations to an admission rate of 1.77% on a ten day lag or 1.4% on a 6 day lag
This is important because you can then project forward the likely number of admissions over the next week or two. We are averaging case numbers of about 160,000 at the moment meaning admissions should average between 2200 and 2800 by the middle of next week.
However, English admission data is more up to date and is looking a little less rosy. We saw a jump in admissions on the 28th and 29th to over 2000 per day, although the average is still around 1500. However, that suggests an admission to case ratio of between 1.8-2.3%. This probably reflects a situation where testing capacity means we are under reporting the actual number of infections by a greater extent. However, it also may indicate that we are seeing an increase in the % of people admitted.
This would not necessarily mean that Omicron is more severe. Rather, throughout the pandemic Case to hospital admissions have fluctuated due to other factors. For example, usually we assume that a higher proportion of older adults will end up in hospital. So, as transmission moves into those age groups we might expect admission rates to increase and for them to remain low when cases are higher among younger adults and children. However, the vaccination of the adult population flips that scenario a little. We may well expect the admission rate to increase due to a greater number of unvaccinated/un-boosted teenagers getting ill. Additionally, those in their 20s-30s will only be beginning to experience the full protection of their booster jabs round about now. My expectation is that the ratio will probably increase over a few weeks and then drop back a little as the full benefits of boosters kick in.
All of this means that it remains difficult to project exactly where both case numbers and admissions will land. There is one ray of light though and that is that whilst cases and admissions have been growing rapidly, the number of people moving into ICU and onto Mechanical Ventilation doesn’t seem to be increasing by anywhere near as much. This measure may lag a bit further but would fit the South African experience. If ICU levels remain low then this will be a good indicator that mortality should be lower too.
All of this means that I would take articles like this panicky article from The Daily Telegraph with a good dose of caution It is true that things remain incredibly uncertain. However, I don’t think the Government have committed to a gamble that has blown up in their face. Indeed, a close reading of the article shows that the headline and introduction are based not on fresh/alarming data but rather on the author’s reading of analysis shared via twitter. Indeed, Dr Andrew Goddard, quoted later in the article who has a better view of the frontline situation than most of us armchair epidemiologists certainly doesn’t seem to share the view of the situation, stating:
I think omicron is hopefully going to be a relatively short sharp shock… Provided the number of hospital admissions as omicron hits the over-65s isn’t too bad, I don’t think there’s going to be as much of an impact on the services as a year ago.”
Dr Andrew Goddard.
That quote should have produced a rather different headline! But to be clear once again, no Mr Nuki hasn’t got his hands on shocking bew data but rather has seen the plotting of data which is in fact, very much in line with the potential scenarios which we were looking at just the other week.**
I think the Government made some significant mistakes in regards to England one again and those may bring a heavy prices. First, their border policy was confusing, a partial closing of the stable door after the horse had bolted. Secondly, requiring people to isolate only once contact with an Omicron case allowed several days for those with Omicron to infect many others. The requirement should have been immediate isolation if a contact tested positive from an LFT regardless of variant. I’m also concerned that they may have been slow to start ramping up NHS surge capacity.
However, I suspect that we are beginning to see evidence thar short of a full, heavy handed lockdown which would have required martial law, there weren’t really any measures that would have stopped this variant in its track. Therefore, encouraging caution, boosting vaccination levels and finding ways to increase NHS capacity was probably not just the best call but probably the only call that the Government could make.
Similarly, I am not sure what else could be done at this stage, after Christmas. We may return to bubbles and masking in schools but I think the evidence is clear that even with such measures it will be impossible to prevent outbreaks amongst the school population and I suspect that closing schools again would prove politically unfeasible. So, I believe that the current course of action remains not so much a gambler’s throw of the die but the only approach the government can follow.
I remain nervously and cautiously optimistic that we will see cases peak within the next few weeks and that the boosters will keep admissions down to a difficult but survivable number. The NHS will be stretched though and it is going to be a challenging start to the year.
We will know soon enough!
[1] Whilst you would think that it would be a straight forward case of people calling an ambulance when they couldn’t breath I think it is a little bit more complex than that. My own experience as an asthmatic is that you can battle on for a period of time struggling to breath and with oxygen saturation levels lower than ideal. I’ve also seen families reluctant to get medical help. At the other end of the spectrum, anxiety may encourage people to turn up at A&E when they are confident of being seen as a precautionary measure. This is why I have suspected that the lag time between positive test and admission may vary a bit through stages of the pandemic.
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** In the article I set out several scenarios. This was the mediating scenario
As you can see, I was expecting average cases of around 160k by this week and average admissions of at least 2.4k we are probably not going to be too far off that in terms of cases, whilst admissions (note these will be for next Sunday based on a 6 day lag) will probably be around the 3k mark suggesting a 2% admission rate.
Faithroots 